The present invention generally relates to headgear and, more specifically, to a protective helmet for recreational activities such as skiing, snowboarding, bicycling, rollerblading, skateboarding, horseback riding, rock climbing, spelunking and the like.
Protective helmets for recreational activities, competitive sports, motor sports and other endeavors where a chance of cranial impact is possible are known in the art. Although no helmet is capable of preventing accidents and no helmet can completely prevent injury during an accident, the prior art helmets, particularly those designed for recreational sports, have many disadvantages. One common disadvantage is that many helmets block the wearer's hearing and peripheral visual abilities. This detracts from the wearer's ability to avoid accidents and dangerous situations that may have otherwise been seen or heard in time to react.
Another disadvantage is that many helmets provide a shell that is too weak to provide effective protection from a sudden impact. A good helmet protects the head by distributing the energy, or force, of an impact around the shell of the helmet. The shell, in turn, transfers the energy to an energy absorbing liner. The liner is capable of absorbing more energy if the force is distributed over a greater area of the liner. More energy absorbed by the liner means that less energy will be transferred to the wearer's head. To do this, the shell of the helmet needs to be stiff. If the helmet is not stiff enough, the impact will deflect the shell of the helmet in the area of the impact. In that case, the energy will be transferred to the liner in a more localized manner, resulting in a high force per unit of area that is likely to or could cause greater injury than if the force were more distributed.
Most conventional ski and bicycling helmets have a solid shell of a fixed size made from thermoplastic resins, such as polycarbonate, ABS, acrylic or vinyl. These types of shells have a low elastic modulus (i.e., 300,000 psi), a low flexural strength (i.e., 340,000 psi) and a high percentage elongation at break (i.e., 125%). These parameters are not very conducive to protecting a head against impact. Most of these helmets will deflect a greater amount under impact and transfer the energy of the impact through or into the liner material in a smaller area than would happen if the helmet shell was stronger, stiffer, and/or had less elongation. In addition, the mold cycle for these shells is comparatively long (i.e., 1 to 1.5 minutes).
Another disadvantage of many helmets is the adequacy of the helmet's fit to the wearer's head. Most prior art helmets for recreational sports have many sizing disadvantages. The retailers need to stock sometimes 8 or more sizes relating to head circumference measurements between approximately 19.7 inches to 24.4 inches (or 50 cm and 62 cm). Furthermore, even if two people have heads of the same circumference, their heads can easily vary in width by half an inch. The result is that a person with a wide head would have to buy a helmet that is too long and a person with a long head would have to buy a helmet that is too wide. The traditional solution to this problem is to provide many helmet sizes, typically all with the same width to length ratio, and include a kit of add-in, non-energy absorbing foam to consume any extra space. However, this approach provides for a larger helmet shell than is needed. If the helmet receives an oblique impact, the moment on the helmet will be greater than on a smaller helmet, resulting in more torque being transferred to the wearer's neck. In such a situation, the possibility for, and the severity of, neck and spinal injuries increases.
Another approach for achieving a tight fit is to provide a helmet with an elastic textile that compresses tiles of rigid shell pieces that are supported by an energy absorbing foam. This is similar to a skullcap with an elastic compressing device. This type of helmet is not easily adjusted as it is designed to compress itself to the smallest size possible and, therefore, tends to be uncomfortably tight on the wearer. To provide more comfort to the wearer, the foam can be made softer and the outer shell more flexible. However, softer and more flexible materials do not absorb energy well and decrease the performance of the helmet.
Another method to achieve a tight fit is to provide an inflatable air bladder and/or energy absorbing foam pads between the wearer and the inside of the helmet. Air bladder helmets have a tendency to rebound or bounce, meaning they store the energy of an impact and then redeliver the energy in the opposite direction. Consequently, air bladders are sufficient to absorb low speed impacts of approximately 10 miles per hour or less as experience in football, lacrosse and hockey. However, air bladders are not particularly effective at absorbing the energy of a higher speed impact.